view mod_s2s_auth_dane/mod_s2s_auth_dane.lua @ 4340:7cd3b7ec59e9

mod_http_oauth2: Rudimentary support for scopes (but not really) We don't support limiting access, but this change will inform the client what permissions the created token has (e.g. is the user an admin or not). There is some work in progress on real scope support.
author Matthew Wild <mwild1@gmail.com>
date Sat, 16 Jan 2021 19:47:22 +0000
parents 77498ea07795
children cf2bdb2aaa57
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-- mod_s2s_auth_dane
-- Copyright (C) 2013-2014 Kim Alvefur
--
-- This file is MIT/X11 licensed.
--
-- Implements DANE and Secure Delegation using DNS SRV as described in
-- http://tools.ietf.org/html/draft-miller-xmpp-dnssec-prooftype
--
-- Known issues:
-- Could be done much cleaner if mod_s2s was using util.async
--
-- TODO Things to test/handle:
-- Negative or bogus answers
-- No encryption offered
-- Different hostname before and after STARTTLS - mod_s2s should complain
-- Interaction with Dialback
--
-- luacheck: ignore module

module:set_global();

local have_async, async = pcall(require, "util.async");
local noop = function () end
local type = type;
local t_insert = table.insert;
local set = require"util.set";
local dns_lookup = require"net.adns".lookup;
local hashes = require"util.hashes";
local base64 = require"util.encodings".base64;
local idna_to_ascii = require "util.encodings".idna.to_ascii;
local idna_to_unicode = require"util.encodings".idna.to_unicode;
local nameprep = require"util.encodings".stringprep.nameprep;
local cert_verify_identity = require "util.x509".verify_identity;

do
	local net_dns = require"net.dns";
	if not net_dns.types or not net_dns.types[52] then
		module:log("error", "No TLSA support available, DANE will not be supported");
		return
	end
end

local pat = "%-%-%-%-%-BEGIN ([A-Z ]+)%-%-%-%-%-\r?\n"..
"([0-9A-Za-z=+/\r\n]*)\r?\n%-%-%-%-%-END %1%-%-%-%-%-";
local function pem2der(pem)
	local typ, data = pem:match(pat);
	if typ and data then
		return base64.decode(data), typ;
	end
end
local use_map = { ["DANE-EE"] = 3; ["DANE-TA"] = 2; ["PKIX-EE"] = 1; ["PKIX-CA"] = 0 }

local implemented_uses = set.new { "DANE-EE", "PKIX-EE" };
do
	local cert_mt = debug.getregistry()["SSL:Certificate"];
	if cert_mt and cert_mt.__index.issued then
		-- Need cert:issued() for these
		implemented_uses:add("DANE-TA");
		implemented_uses:add("PKIX-CA");
	else
		module:log("debug", "The cert:issued() method is unavailable, DANE-TA and PKIX-CA can't be enabled");
	end
	if not cert_mt.__index.pubkey then
		module:log("debug", "The cert:pubkey() method is unavailable, the SPKI usage can't be supported");
	end
end
local configured_uses = module:get_option_set("dane_uses", { "DANE-EE", "DANE-TA" });
local enabled_uses = set.intersection(implemented_uses, configured_uses) / function(use) return use_map[use] end;
local unsupported = configured_uses - implemented_uses;
if not unsupported:empty() then
	module:log("warn", "Unable to support DANE uses %s", tostring(unsupported));
end

-- Find applicable TLSA records
-- Takes a s2sin/out and a callback
local function dane_lookup(host_session, cb)
	cb = cb or noop;
	local log = host_session.log or module._log;
	if host_session.dane ~= nil then return end -- Has already done a lookup

	if host_session.direction == "incoming" then
		if not host_session.from_host then
			log("debug", "Session doesn't have a 'from' host set");
			return;
		end
		-- We don't know what hostname or port to use for Incoming connections
		-- so we do a SRV lookup and then request TLSA records for each SRV
		-- Most servers will probably use the same certificate on outgoing
		-- and incoming connections, so this should work well
		local name = host_session.from_host and idna_to_ascii(host_session.from_host);
		if not name then
			log("warn", "Could not convert '%s' to ASCII for DNS lookup", tostring(host_session.from_host));
			return;
		end
		log("debug", "Querying SRV records from _xmpp-server._tcp.%s.", name);
		host_session.dane = dns_lookup(function (answer, err)
			host_session.dane = false; -- Mark that we already did the lookup

			if not answer then
				log("debug", "Resolver error: %s", tostring(err));
				return cb(host_session);
			end

			if answer.bogus then
				log("warn", "Results are bogus!");
				-- Bad sign, probably not a good idea to do any fallback here
				host_session.dane = answer;
			elseif not answer.secure then
				log("debug", "Results are not secure");
				return cb(host_session);
			end

			local n = answer.n or #answer;
			if n == 0 then
				-- No SRV records, synthesize fallback host and port
				-- this may behave oddly for connections in the other direction if
				-- mod_s2s doesn't keep the answer around
				answer[1] = { srv = { target = name, port = 5269 } };
				n = 1;
			elseif n == 1 and answer[1].srv.target == '.' then
				return cb(host_session); -- No service ... This shouldn't happen?
			end
			local srv_hosts = { answer = answer };
			host_session.srv_hosts = srv_hosts;
			local dane;
			for _, record in ipairs(answer) do
				t_insert(srv_hosts, record.srv);
				log("debug", "Querying TLSA record for %s:%d", record.srv.target, record.srv.port);
				dns_lookup(function(dane_answer)
					log("debug", "Got answer for %s:%d", record.srv.target, record.srv.port);
					n = n - 1;
					-- There are three kinds of answers
					-- Insecure, Secure and Bogus
					--
					-- We collect Secure answers for later use
					--
					-- Insecure (legacy) answers are simply ignored
					--
					-- If we get a Bogus (dnssec error) reply, keep the
					-- status around.  If there were only bogus replies, the
					-- connection will be aborted.  If there were at least
					-- one non-Bogus reply, we proceed.  If none of the
					-- replies matched, we consider the connection insecure.

					if (dane_answer.bogus or dane_answer.secure) and not dane then
						-- The first answer we care about
						-- For services with only one SRV record, this will be the only one
						log("debug", "First secure (or bogus) TLSA")
						dane = dane_answer;
					elseif dane_answer.bogus then
						log("debug", "Got additional bogus TLSA")
						dane.bogus = dane_answer.bogus;
					elseif dane_answer.secure then
						log("debug", "Got additional secure TLSA")
						for _, dane_record in ipairs(dane_answer) do
							t_insert(dane, dane_record);
						end
					end
					if n == 0 then
						if dane then
							host_session.dane = dane;
							if #dane > 0 and dane.bogus then
								-- Got at least one non-bogus reply,
								-- This should trigger a failure if one of them did not match
								log("warn", "Ignoring bogus replies");
								dane.bogus = nil;
							end
							if #dane == 0 and dane.bogus == nil then
								-- Got no usable data
								host_session.dane = false;
							end
						end
						return cb(host_session);
					end
				end, ("_%d._tcp.%s."):format(record.srv.port, record.srv.target), "TLSA");
			end
		end, "_xmpp-server._tcp."..name..".", "SRV");
		return true;
	elseif host_session.direction == "outgoing" then
		-- Prosody has already done SRV lookups for outgoing session, so check if those are secure
		local srv_hosts = host_session.srv_hosts;
		if not ( srv_hosts and srv_hosts.answer and srv_hosts.answer.secure ) then
			return; -- No secure SRV records, fall back to non-DANE mode
			-- Empty response were not kept by older mod_s2s/s2sout
		end
		-- Do TLSA lookup for currently selected SRV record
		local srv_choice = srv_hosts[host_session.srv_choice or 0] or { target = idna_to_ascii(host_session.to_host), port = 5269 };
		log("debug", "Querying TLSA record for %s:%d", srv_choice.target, srv_choice.port);
		host_session.dane = dns_lookup(function(answer)
			if answer and ((answer.secure and #answer > 0) or answer.bogus) then
				srv_choice.dane = answer;
			else
				srv_choice.dane = false;
			end
			host_session.dane = srv_choice.dane;
			return cb(host_session);
		end, ("_%d._tcp.%s."):format(srv_choice.port, srv_choice.target), "TLSA");
		return true;
	end
end

local function pause(host_session)
	host_session.log("debug", "Pausing connection until DANE lookup is completed");
	host_session.conn:pause()
end

local function resume(host_session)
	host_session.log("debug", "DANE lookup completed, resuming connection");
	host_session.conn:resume()
end

if have_async then
	function pause(host_session)
		host_session.log("debug", "Pausing connection until DANE lookup is completed");
		local wait, done = async.waiter();
		host_session._done_waiting_for_dane = done;
		wait();
	end
	local function _resume(_, host_session)
		if host_session._done_waiting_for_dane then
			host_session.log("debug", "DANE lookup completed, resuming connection");
			host_session._done_waiting_for_dane();
			host_session._done_waiting_for_dane = nil;
		end
	end
	function resume(host_session)
		-- Something about the way luaunbound calls callbacks is messed up
		if host_session._done_waiting_for_dane then
			module:add_timer(0, _resume, host_session);
		end
	end
end

function module.add_host(module)
	local function on_new_s2s(event)
		local host_session = event.origin;
		if host_session.type == "s2sout" or host_session.type == "s2sin" then
			return; -- Already authenticated
		end
		if host_session.dane ~= nil then
			return; -- Already done DANE lookup
		end
		dane_lookup(host_session, resume);
		-- Let it run in parallel until we need to check the cert
	end

	-- New outgoing connections
	module:hook("stanza/http://etherx.jabber.org/streams:features", on_new_s2s, 501);
	module:hook("s2sout-authenticate-legacy", on_new_s2s, 200);

	-- New incoming connections
	module:hook("s2s-stream-features", on_new_s2s, 10);

	module:hook("s2s-authenticated", function(event)
		local session = event.session;
		if session.dane and type(session.dane) == "table" and next(session.dane) ~= nil and not session.secure then
			-- TLSA record but no TLS, not ok.
			-- TODO Optional?
			-- Bogus replies should trigger this path
			-- How does this interact with Dialback?
			session:close({
				condition = "policy-violation",
				text = "Encrypted server-to-server communication is required but was not "
					..((session.direction == "outgoing" and "offered") or "used")
			});
			return false;
		end
		-- Cleanup
		session.srv_hosts = nil;
	end);
end

-- Compare one TLSA record against a certificate
local function one_dane_check(tlsa, cert, log)
	local select, match, certdata = tlsa.select, tlsa.match;

	if select == 0 then
		certdata = pem2der(cert:pem());
	elseif select == 1 and cert.pubkey then
		certdata = pem2der(cert:pubkey());
	else
		log("warn", "DANE selector %s is unsupported", tlsa:getSelector() or select);
		return;
	end

	if match == 1 then
		certdata = hashes.sha256(certdata);
	elseif match == 2 then
		certdata = hashes.sha512(certdata);
	elseif match ~= 0 then
		log("warn", "DANE match rule %s is unsupported", tlsa:getMatchType() or match);
		return;
	end

	if #certdata ~= #tlsa.data then
		log("warn", "Length mismatch: Cert: %d, TLSA: %d", #certdata, #tlsa.data);
	end
	return certdata == tlsa.data;
end

module:hook("s2s-check-certificate", function(event)
	local session, cert, host = event.session, event.cert, event.host;
	if not cert then return end
	local log = session.log or module._log;
	local dane = session.dane;
	if type(dane) ~= "table" then
		if dane == nil and dane_lookup(session, resume) then
			pause(session);
			dane = session.dane;
		end
	end
	if type(dane) == "table" then
		local match_found, supported_found;
		for i = 1, #dane do
			local tlsa = dane[i].tlsa;
			log("debug", "TLSA #%d: %s", i, tostring(tlsa))
			local use = tlsa.use;

			if enabled_uses:contains(use) then
				-- DANE-EE or PKIX-EE
				if use == 3 or use == 1 then
					-- Should we check if the cert subject matches?
					local is_match = one_dane_check(tlsa, cert, log);
					if is_match ~= nil then
						supported_found = true;
					end
					if is_match and use == 1 and session.cert_chain_status ~= "valid" then
						-- for usage 1, PKIX-EE, the chain has to be valid already
						log("debug", "PKIX-EE TLSA matches untrusted certificate");
						is_match = false;
					end
					if is_match then
						log("info", "DANE validated ok for %s using %s", host, tlsa:getUsage());
						session.cert_identity_status = "valid";
						if use == 3 then -- DANE-EE, chain status equals DNSSEC chain status
							session.cert_chain_status = "valid";
						end
						match_found = true;
						dane.matching = tlsa;
						break;
					end
				-- DANE-TA or PKIX-CA
				elseif use == 2 or use == 0 then
					supported_found = true;
					local chain = session.conn:socket():getpeerchain();
					for c = 1, #chain do
						local cacert = chain[c];
						local is_match = one_dane_check(tlsa, cacert, log);
						if is_match ~= nil then
							supported_found = true;
						end
						if is_match and not cacert:issued(cert, unpack(chain)) then
							is_match = false;
						end
						if is_match and use == 0 and session.cert_chain_status ~= "valid" then
							-- for usage 0, PKIX-CA, identity and chain has to be valid already
							is_match = false;
						end
						if is_match then
							log("info", "DANE validated ok for %s using %s", host, tlsa:getUsage());
							if use == 2 then -- DANE-TA
								session.cert_identity_status = "valid";
								if cert_verify_identity(host, "xmpp-server", cert) then
									session.cert_chain_status = "valid";
									-- else -- TODO Check against SRV target?
								end
							end
							match_found = true;
							dane.matching = tlsa;
							break;
						end
					end
					if match_found then break end
				end
			end
		end
		if supported_found and not match_found or dane.bogus then
			-- No TLSA matched or response was bogus
			local why = "No TLSA matched certificate";
			if dane.bogus then
				why = "Bogus: "..tostring(dane.bogus);
			end
			log("warn", "DANE validation failed for %s: %s", host, why);
			session.cert_identity_status = "invalid";
			session.cert_chain_status = "invalid";
		end
	else
		if session.cert_chain_status == "valid" and session.cert_identity_status ~= "valid"
		and session.srv_hosts and session.srv_hosts.answer and session.srv_hosts.answer.secure then
			local srv_hosts, srv_choice, srv_target = session.srv_hosts, session.srv_choice;
			for i = srv_choice or 1, srv_choice or #srv_hosts do
				srv_target = session.srv_hosts[i].target:gsub("%.?$","");
				log("debug", "Comparing certificate with Secure SRV target %s", srv_target);
				srv_target = nameprep(idna_to_unicode(srv_target));
				if srv_target and cert_verify_identity(srv_target, "xmpp-server", cert) then
					log("info", "Certificate for %s matches Secure SRV target %s", host, srv_target);
					session.cert_identity_status = "valid";
					return;
				end
			end
		end
	end
end);

-- Telnet command
if module:get_option_set("modules_enabled", {}):contains("admin_telnet") then
	module:depends("admin_telnet"); -- Make sure the env is there
	local def_env = module:shared("admin_telnet/env");

	local function annotate(session, line)
		line = line or {};
		table.insert(line, "--");
		if session.dane == nil then
			table.insert(line, "No DANE attempted, probably insecure SRV response");
		elseif session.dane == false then
			table.insert(line, "DANE failed or response was insecure");
		elseif type(session.dane) ~= "table" then
			table.insert(line, "Waiting for DANE records...");
		elseif session.dane.matching then
			table.insert(line, "Matching DANE record:\n|       " .. tostring(session.dane.matching));
		else
			table.insert(line, "DANE records:\n|       " .. tostring(session.dane));
		end
		return table.concat(line, " ");
	end

	function def_env.s2s:show_dane(...)
		return self:show(..., annotate);
	end
end